IE Windows vuln coughs up local files

One click bares entire C drive

If you use any version of Internet Explorer to surf Twitter or other Web 2.0 sites, Jorge Luis Alvarez Medina can probably read the entire contents of your primary hard drive.

The security consultant at Core Security said his attack works by clicking on a single link that exploits a chain of weaknesses in IE and Windows. Once an IE user visits the booby-trapped site, the webmaster has complete access to the machine's C drive, including files, authentication cookies - even empty hashes of passwords.

This isn't the first time security researchers at Core have identified security weaknesses in IE. The company issued this advisory in 2008 and this one in 2009, each identifying specific links in the chain that could potentially be abused by an attacker.

"Every time we reported this to Microsoft, they were fixing just one of the features," Medina said in a telephone interview from Bueno Aires. "Every time they [fixed] it, we managed another way to build the attack again."

Medina said he has fully briefed Microsoft on his latest attack, which he plans to demonstrate at next month's Black Hat security conference in Washington, DC. Microsoft's "rapid response team" didn't reply to an email, but a statement sent to other news outlets said the company is investigating the vulnerability and isn't aware of it being exploited in the wild.

The hole is difficult to close because the attack exploits an array of features IE users have come to rely on to make web application work seamlessly. Simply removing the features could neuter functions such as online file sharing and active scripting, underscoring the age-old tradeoff between a system's functionality and its security.

Based on Medina's characterization, it appears that fixing the weakness will require changes in a Windows network sharing technology known as SMB, or server message block, as well as the way Windows makes file caches available to a wide variety of applications.

"The things we are reporting are not bugs, they are features," Medina said. "They are needed for many applications to work, so [Microsoft] can't simply remove or truncate" them.

IE suffers from at least one other long-standing security bug that can enable attacks against people browsing websites that are otherwise safe to view. It can be exploited to introduce XSS, or cross-site scripting, exploits on webpages, allowing attackers to inject malicious content and code. Microsoft has said it's unaware of this vulnerability being exploited.

Core's previous advisories contain a number of workarounds, including setting the security level for the internet and intranet zones to high to prevent IE from running scripts or ActiveX controls. ®